The present invention relates to a bottom vacuum corrugated feeder, and more specifically, to a downhill bottom vacuum corrugated feeder which enables feeding of intermixed size documents in a document handler of an image producing device, and a method of feeding a document from a stack of intermixed size documents to a document handler.
With the advent of high speed copy reproduction machines wherein copies can be produced at a rate in excess of three thousand copies per hour, there is a need for a document handler to feed documents to the copy platen of the machine in a rapid, dependable manner to enable full utilization of the reproduction machine's potential copy output. A number of document handlers are currently available to fill that need. These document handlers must operate flawlessly to virtually eliminate the risk of damaging the originals and generate minimum machine shutdowns due to uncorrectable misfeeds or document multifeeds. It is in the initial separation of the individual documents from the document stack where the greatest number of problems occur.
Since the documents must be handled gently but positively to assure separation without damage through a number of cycles, a number of separators have been suggested such as friction rolls or belts used for fairly positive document feeding in conjunction with a retard belt, pad or roll to prevent multifeeds. Vacuum separators such as sniffer tubes, rocker type vacuum rolls or vacuum feed belts have also been utilized.
While the friction roll-retard systems are very positive, the action of the retard member, if it acts upon the printed face, can cause smearing or partial erasure of the printed material on the document. With single sided documents, this does not present a problem as the separator can be designed so that the retard mechanism acts upon the underside of the document. However, with documents printed on both sides, there is no way to avoid the problem. Additionally, the reliable operation of friction retard feeders is highly dependent on the relative frictional properties of the paper being handled. This cannot be controlled in a document feeder.
A typical vacuum separating and feeding system is that described in U.S. Pat. No. 4,305,576 entitled "Sheet Separator" to Hamlin, wherein a plurality of friction belts is arranged to run over a vacuum plenum placed at the bottom of a sheet supply tray which has a "U" shaped pocket formed in it. The pocket serves to provide space for the bottom sheet to be captured by the vacuum feed belt assembly, to provide an air seal between the bottom document and the edges of the pocket and to provide a high pressure seal between the bottom sheet and the remainder of the stack. This high pressure seal is achieved by supporting a major portion of the stack weight on the edge regions of the pocket. This seal serves to convert the velocity energy of the air knife flow into a lifting pressure over the pocket area to levitate the remainder of the stack of sheets. This configuration has been used on a commercial scale in the Xerox 5600 machine, and while it has been highly successful in operation, certain aspects can be improved. In particular, the operating window for air knife pressure and stack weight is relatively low which when exceeded causes an unstable pocket to exist. This is manifested by the second sheet vibrating independent of the rest of the stack in a manner referred to as "flutter" and is caused by an aerodynamic instability due to a very low angle of attack of the air knife relative to the stack together with the springness of the sheet. As a result there is a dynamic bouncing of sheet two on sheet one and while it is not coincident with sheet one, sheet two will tend to shingle out of the stack with sheet one resulting in a multifeed. In addition, since the bottommost sheet and sheet two are in the same plane and with sheet two and the remainder of the stack resting on the bottommost sheet, difficulty in separating the bottommost sheet from sheet two can be encountered. This is because there may be some frictional bonding between the bottommost sheet and sheet two.
Further, the operating window of air knife pressure and stack height or weight is low since for additional stack height or weight increments the air knife pressure must be increased thereby increasing the possibility of blowback where the topmost sheet is blown off the stack. Higher air knife pressures are desired since increased amounts of air and increased air pressure increase the reliability of separation of the bottommost sheet from the rest of the stack by providing better levitation of the stack. An additional problem that may be encountered is that of lead edge curl when the lead edge of the sheet being fed may not be captured by the vacuum transport resulting in damage to the sheet and possible misfeed. Furthermore, in addition to the flutter described above, with large stacks the stack of sheets as a whole may flutter or gallop.
In summary, in the bottom sheet feeders difficulties are encountered in both separating the bottommost sheet from the remainder of the stack of sheets and in levitating the remainder of the stack. Moreover, typical vacuum feeders are limited for extended copy jobs in that the feeder assembly can only accommodate a uniform size paper stack. Although the tray can be adjusted to accommodate more than one document size, the apparatuses cannot accommodate for an intermixed size document stack.
Similar problems with regard to separation exist in top sheet vacuum feeders although the necessity to levitate the stack of sheets is not present. In this configuration the air injection means is used to hold the stack of sheets down so that flutter and its attendent multifeed will not occur.
U.S. Pat. No. 3,424,453 (Halbert) illustrates a vacuum sheet separator feeder with an air knife wherein a plurality of feed belts with holes are transported about a vacuum plenum and pressurized air is delivered to the leading edge of the stack of sheets.
U.S. Pat. No. 2,594,373 (Watson) illustrates a sheet separator with two nozzles wherein each nozzle has two vertically elongated jets which impinge on deflecting surfaces at the mouth of the nozzle to deflect air centrally toward the nozzle mouth which creates a highly turbulent forward moving blast of air. The device is used to separate the rear edge of a stack of sheets as the sheet is advanced forwardly by suckers.
U.S. Pat. No. 3,294,396 (Staines) discloses two sets of air nozzles at the rear of a stack of sheets to be fed, one set to separate the sheets from the stack and the other to float the sheet.
U.S. Pat. No. 3,079,149 (Childs) illustrates the top sheet feeder in which a stream of air rifles a stack of sheets so that the top sheet can be picked up by a vacuum arm. Air rushing into a vacuum duct is used to hold the edges of a sheet down while they are being separated along a different edge.
U.S. Pat. No. 2,402,442 (Perry) describes a sheet separating device containing a baffle which directs two jets of air at the outer edges of a stack of paper. The baffle sets up "whirling" air currents under the top sheet which separates it from the lower lying sheet.
U.S. Pat. No. 3,980,293 (Shelmire) discloses a sheet separating mechanism in which the rear of the top sheet is initially lifted with a vacuum arm followed by air blasts from the rear and front which provide an air cushion between the first and second sheets. The device also incorporates hold-down feed for sheets underlying the topmost sheet.
U.S. Pat. Nos. 4,418,905 (Garavuso) and 4,462,586 (Browne et al.) disclose a vacuum corrugating feeder air knife, and a tray for a recirculating document handler RDH. The operation of the vacuum channel of the present invention is substantially similar to that described in the above-mentioned '905 and '586 patents.
All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.